Depending upon the machine and grade being made, the time lost recovering from web breaks is often equal to the down time for maintenance and clothing changes. Re-threading a paper machine following a break typically takes from several minutes to several tens of minutes and, on certain grades an hour is not uncommon. Therefore, papermakers have good reason to refine and improve the apparatus and methods of threading since every minute of lost time on a modern paper machine represents a significant economic penalty.
To affect recovery from a break, a narrow ribbon, referred to as a tail, is continuously cut from the front margin of the full web at a station up-stream from the point where the web broke. Once formed, the leading few feet of the tail are caused to enter the tail conveying ropes of the downstream section; a conveyor comprised of two endless ropes that trace the process path of each section. The following footage of the tail are thereby pulled through the path of the downstream section.
After the tail arrives at the outlet end of the rope conveyor, the speed of the downstream section is increased to first remove slack and then to establish normal running tension. Throughout this phase, and roughly in proportion to the progressive application of tension, the operator widens the tail to reduce the risk of its breaking. A section is successfully threaded when the tail obtains the width of the main web.
The same procedures are repeated at each following machine section until the full web is returned to the reel.